Some I keep forever (I have the first fly I ever tied) but most of them get fished. The worst you can do with a streamer is get the head wrong, too big, bad shape etc.

With dries it's different, the wings might be too big or tilted too forward, still I used them unless they were so bad that I was shamed by them. I guess that's how you get good, you keep tying flies until what you don't think is any good your friends will jump at. Never quit trying to tie better flies.